City dwellers tend to think of themselves as greener than the rest of the country—less driving means lower carbon emissions, apartments leave a smaller footprint than single-family houses. But there’s one aspect of city life that actually produces more greenhouse gas than driving: throwing away leftovers at the back of the fridge instead of using a kitchen food waste disposer, or, even better, composting. A massive amount of food—35 million tons—winds up in landfill in the U.S. every year according to the EPA, with the vast majority of it coming from urban areas. It’s not just homes but restaurants, supermarkets, hospitals, schools and corporate cafeterias contributing to the problem. Add it all up and the United States wastes an astonishing 30 to 40 percent of our abundant food supply.

Almost all of this wasted food winds up in landfill. As one ton of food decomposes, it generates another ton of methane, which traps heat in the atmosphere even more than carbon dioxide. The Intergovernmental Panel on Climate Change (IPCC) calculates that for the next 20 years, methane will be 72 times more harmful than carbon dioxide in its impact on climate change. One ton of methane released into the atmosphere is the equivalent of a 2,400 mile road trip–from New York City to Phoenix, based on the EPA’s Waste Reduction Model.

Many of the most devoted foodies do not make this connection. We may make an effort to buy organic carrots, but we don’t think twice about throwing the peelings and the tops into the trash. 180 cities are already offering curbside pickup of food scraps, but the reception to Mayor Michael Bloomberg’s plan for mandatory composting in New York City–arguably the food capital of the U.S.–has been lukewarm at best. New Yorkers have expressed concern about fitting a composting bin into a small kitchen, the smell, and the potential for vermin.

Meanwhile, the restaurant world is feeling similarly challenged, even though establishments in San Francisco, Seattle and Portland have been able to accommodate mandatory composting. Some New York restaurants say that they have no space to separate and store the food waste, and even the most environmentally-friendly restaurants such as Blue Hill have expressed concern about the logistics.

Enjoying a huge variety of food has always been a part of the urban experience, one of its big selling points. But now New Yorkers need to take as much responsibility in the way they discard food as in how they consume it.